Revert of IPC: Add attachment brokering support to the message header.

Revert of IPC: Add attachment brokering support to the message header. (patchset #20 id:420001 of https://codereview.chromium.org/1286253002/ )

Reason for revert:
Suspected of breaking XP Tests. See, for example https://build.chromium.org/p/chromium.win/builders/XP%20Tests%20%281%29/builds/39586 .

Original issue's description:
> IPC: Add attachment brokering support to the message header.
>
> Message dispatch happens before message translation, and message dispatch
> requires that all brokered attachments have been received. This means that
> attachment brokering needs to function without message translation. This is
> accomplished by modifying the message header to include a new field
> num_brokered_attachments, and writing the attachment ids into the IPC Channel
> immediately following the pickled message itself.
>
> AttachmentBrokerPrivilegedWinUnittest was expanded to test ChannelReader in the
> receiving process. It is now a fully functional end-to-end test of attachment
> brokering.
>
> BUG=493414
>
> Committed: https://crrev.com/e8e4f4fa67ee9db6c2910020ef49318e5df68481
> Cr-Commit-Position: refs/heads/master@{#344389}

TBR=tsepez@chromium.org,thakis@chromium.org,erikchen@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=493414
Committed: https://crrev.com/16e26d48963f94a6412f9b58587b285cd9ca5695
Cr-Commit-Position: refs/heads/master@{#344461}

[Adam Rice, 2015-08-20 09:21:17]

Created Revert of IPC: Add attachment brokering support to the message header.

[commit-bot: I haz the power, 2015-08-20 09:21:49]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1286883003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1286883003/1

[commit-bot: I haz the power, 2015-08-20 09:22:29]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-08-20 09:23:01]

Patchset 1 (id:??) landed as
https://crrev.com/16e26d48963f94a6412f9b58587b285cd9ca5695
Cr-Commit-Position: refs/heads/master@{#344461}